Retroreflective inks

ABSTRACT

The combination of ingredients, especially for use in the formulation of a one or two-pack retroreflective ink, comprising retroreflective elements, microbeads additional to said retroreflective elements and/or constituting said retroreflective elements at least in part, binder chemicals for attaching the retroreflective elements and microbeads to a substrate to which the ink is to be applied, and a coupling agent for coupling the microbeads and cross-linking the binder chemicals, the coupling agent being unreactive until the printing process is carried out.

Retroreflective coating compositions have been the subject of numerouspatents, for example U.S. Pat. No. 2,963,378, Palmquist et al, U.S. Pat.Nos. 3,099,637, 3,228,897 and 3,420,597, Nellessen, U.S. Pat. No.3,535,019, Longlet et al and U.S. Pat. Nos. 4,103,060 and 4,263,345,Bingham et al. A retroreflective ink has been commercially available fora number of years, marketed by the 3M company, this product beingavailable in dark grey and sold as a three pack system, comprising abinder dispersion system, a pack of hemispherically coated glassmicrospheres or beads and a coupling agent, which are mixed just priorto use.

One pack inks were proposed in WO 94/06869, M N Ellis and in EP 0 729592, Reflective Technology Industries Limited and U.S. Pat. No.5,650,213, Reflective Technology Inc., which also disclose theincorporation of pigment. U.S. Pat. No. 5,650,213 specified a range ofpigment particle size which is what is, in fact, the usual rangecommercially available, and ranges of binder/bead and binder/(bead andpigment) volume ratios which are seemingly the ranges of choice toproduce an ink which is printable by conventional screen printingtechniques.

Problems associated with the performance of reflective coatings,especially in the convenient, one-pack form that does not require mixingjust prior to printing, involve shelf life, washfastness and abrasionresistance. These key areas are interrelated—the binder system must besuch as will not allow the beads to settle even over extended storageperiods, and it must also not couple to the beads during that storage,yet it must, on printing, adhere the beads to the substrate in areasonably washfast and abrasion resistant manner while permitting thebeads to be exposed appropriately to retroreflect light.

The severity of these problems may explain the sale by 3M of the threepack system and the fact that the inks produced according to U.S. Pat.No. 5,650,213 are formulated solely for the production of printed fabricby the patentee Reflective Technology Inc. and not for sale to printers.

The present invention addresses these—and other—problems and provideslong shelf life one pack retroreflective ink systems with goodwashfastness and abrasion resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic flow diagram of one specific embodiment of amethod of forming a retroreflective ink in accordance with the presentinvention.

FIG. 2 is a block diagram of another specific embodiment of the methodof forming a retroreflective ink in accordance with the presentinvention.

According to one aspect of the present invention there is provided thecombination of ingredients, especially for use in the formulation of aone or two-pack retroreflective ink, comprising retroreflectiveelements, microbeads additional to said retroreflective elements and/orconstituting said retroreflective elements at least in part, binderchemicals for attaching the retroreflective elements and microbeads to asubstrate to which the ink is to be applied, and a coupling agent forcoupling the microbeads and cross-linking the binder chemicals, thecoupling agent being unreactive until the printing process is carriedout.

A one-pack ink produced using the above combination of ingredients mayhave a storage life of not less than 3 months, preferably not less than6 months and more preferably not less than 12 months when stored underambient conditions (i.e. a temperature of about 20° C.). Also such inks,when stored for prolonged periods of 3 months or more under ambientconditions, show no significant change in rheology while retainingadequate retroreflectivity properties and durability to laundering.Thus, a retroreflective one-pack ink in accordance with the inventionmay retain a viscosity of between 10 and 30 pascal after storage for notless than 3 months, preferably not less than 6 months and morepreferably not less than 12 months, and may also exhibit launderingdurability such that retroreflectivity is not reduced by more than 40%(preferably by not more than 30% and more preferably by not more than20%) when applied to a substrate in the form of a cotton, nylon orpolyester and laundered for 5 cycles in accordance with ISO 6330, method5A.

The coupling agent is usually one which is substantially unreactive atambient temperature, namely 20° C. Typically the coupling agent isunreactive except at elevated temperature at which the printed substrateis cured, e.g. a temperature within the range of 60 to 200° C., e.g. 130to 180° C.

The coupling agent may be rendered active by elevated temperature;however, we do not exclude the possibility that the coupling agent maybe rendered active by other means such as exposure to UV light or otherhigh energy radiation.

Typically the binder is polymeric and the coupling agent serves tocouple the beads to the polymeric binder.

Viewed from another aspect, the invention resides in a one-pack or atwo-pack retroreflective ink comprising microbeads in a liquid carriermedium including binder chemicals for attaching the microbeads to asubstrate to which the ink is to be applied, the microbeads beingincorporated in the carrier medium, and a coupling agent which couplesthe microbeads and cross-links the binder chemicals, characterised inthat the coupling agent is not activated until the ink is printed.

The two-pack system comprises a separate pack for the coupling agent.

The ink may comprise retroreflective and/or non-retroreflectivemicrobeads. Typically the proportion of microbeads which do not have aretroreflective coating constitute no more than 50% by volume of thetotal microbead content but may be up to 100% when reflective flakes areused in conjunction with microbeads to provide retroreflectivity.

The binder and coupling agent may be selected from, but is not limitedto, the following combinations:

-   -   polyvinylidene chloride copolymer as binder and (3-aminopropyl)        silanetriol and/or blocked 1, 6 hexamethylene diisocyanate        trimer as coupling agent; an acrylic copolymer as binder and        (3-aminopropyl) silanetriol and/or blocked 1, 6 hexamethylene        diisocyanate trimer as coupling agent; and polyurethane as        binder and blocked 1, 6 hexamethylene diisocyanate trimer as        coupling agent.

The microbeads may have an aluminium coating, and may be pre-treatedwith a silicate before inclusion in the ink. They may for instance bepretreated with sodium silicate. They may be treated with a silane,especially a silane having a reactive group such as an amino group,which treatment may be after a silicate treatment and before inclusionin the ink. A suitable amino silane is bis-[gamma-(trimethoxysilyl)propyl] amine.

The ink may comprise pigment, and may, especially when comprisingpigment, comprise non-retroreflective, which usually meansun-metallised, microbeads. The pigment content is typically up to 5% byweight of the ink.

The microbeads may be pretreated before metallisation with stannouschloride.

The ink may be formulated—as to, e.g. viscosity, particle size—suitablyfor screen printing. The microbeads may have a median size in the rangeof 10 to 100 microns, e.g. 25 to 70 microns. Typically in the case ofinks using metallised retroreflective microbeads, the median size isabout 40 microns whereas in the case of inks using non-retroreflectivemicrobeads in conjunction with other reflective elements such asreflective flake particles, the microbeads typically have a median sizeof about 60 microns.

The microbeads, whether retroreflective or not, are preferably composedof high refractive index glass, such as a titanium/barium based glasswith a refractive index in the range of 1.8 to 2.2, e.g. about 1.9.

The ink may comprise a humectant, which may comprise urea and/or 2,3propane diol, and may be water-based. It may comprise a buffer, toensure an appropriate pH, such buffer, for example, comprising anammonium phosphate buffer or a sodium phosphate buffer. A dispersant mayalso be included, as may a defoamer, a thickening agent, a cross-linkingagent and a softening agent.

Other constituents that may be present in the ink may be selected fromthe group comprising carbon black; UV absorbing material; anti-scuffingagent, optionally a silicone or fluoropolymer; light spill-suppressingagent; anti-static agent and water repellant agent, optionally asilicone or fluoropolymer.

Non-water based inks may also be comprised within the invention. In thiscase, the need to protect the aluminium coating against attack inwater-based media may be less important.

Surprisingly, having regard to the teaching of U.S. Pat. No. 5,650,213,substantially better quality inks—in terms of reflectivity,washfastness, abrasion resistance and shelf life—are produced withbinder to bead volume ratios equal to or less than 50%. Essentially,more beads can be attached using less obscuring binder, more firmly andmore permanently than when the prior art binder to bead ratios are used.

For a screen printing ink, the viscosity is desirably equal to or lessthan 40 pascals, preferably between 10 and 30 pascals, at roomtemperature.

The invention also comprises a method for making a one-packretroreflective ink comprising the steps of:

-   -   making microbeads;    -   suspending the microbeads in a liquid carrier medium;    -   the liquid carrier medium comprising binder chemicals for        attaching the microbeads to a substrate to which the ink is to        be applied and a coupling agent which couples the microbeads and        cross-links the binder chemicals, the coupling agent being        unreactive except at elevated temperature (e.g. within the range        from 60 to 200° C. and usually from 130 to 180° C.) at which the        printed substrate is cured.

The method may involve the application of an aluminium coating to glassmicrobeads. The microbeads may be pretreated with stannous chlorideprior to application of the aluminium coating, and may be treated with adilute solution of stannous chloride.

The microbeads maybe hemispherically metallised in a vacuum metallisingprocess in which they are held on a film with an adhesive coating fortransport through the metallising process, the adhesive coatingcomprising a styrene/butadiene type or other adhesive, which loses itstack when wet. The film may comprise a polyester or polyolefin film.Following metallisation, the film may be passed through an aqueoussolution of citric acid or other aqueous solution with a pK_(a) value ofaround 2, and may be treated ultrasonically to assist in release of themicrobeads from the adhesive surface. In contradistinction to othermethods for attachment of beads for metallisation, this method is easierat least inasmuch as the citric acid bath can be re-used over and overwithout replenishment.

The microbeads may be treated prior to inclusion in the ink with asilicate, which may be a dilute aqueous solution of sodium silicate. Thebeads may also (with or without such sodium silicate treatment) betreated with a silane such as an amino silane prior to inclusion in theink, and such silane treatment may follow the silicate treatment. Aparticularly beneficial amino silane is bis-[gamma-(trimethoxysilyl)propyl] amine. These treatments, severally and collectively, appear toenhance the permanence of the attachment of the aluminium coating to themicrobeads and of the microbeads to the substrate on printing.

An aminoalkyl silanetriol and/or a blocked polyisocyanate may be addedto the liquid carrier medium as coupling agent.

In the event, see below, that a two-pack, rather than a one-pack systemis required, an alkoxysilyl alkyl derivative such as an aminosilane—which could be the same amino silane used to treat themicrobeads—and/or a polyisocyanate (typically where the microbeads areamine treated) may also be added to the liquid carrier medium ascoupling agent.

In the preparation of the ink, a liquid carrier medium may be preparedcomprising binder chemicals and coupling agent, the microbeads beingadded to the medium. A pigment may be added to the medium containing themicrobeads.

Further additive or additives to be incorporated in the liquid carriermedium, may be selected from the group comprising:

pigment; humectant, optionally urea and/or 2,3 propane diol; buffer,optionally based on ammonium or sodium phosphates; dispersant; defoamer;thickening agent; cross-linking agent; softening agent; carbon black; UVabsorbing material; anti-scuffing agent, optionally a silicone orfluoropolymer; light spill-suppressing agent; anti-static agent andwater repellant agent, optionally a silicone or fluoropolymer.

Where a thickener is included, it may be added to the medium in twosteps, namely before and after the addition of the binder and coupler.

According to a further aspect of the invention there is providedmicrobeads for use in the production of a retroreflective ink, themicrobeads having silicate (optionally sodium silicate) and/or silane(optionally an amino silane such as bis-[gamma-(trimethoxysilyl) propyl]amino) and/or stannous chloride applied thereto.

The microbeads may be metallised, optionally with a coating ofaluminium, the metal being superposed on the stannous chloride.

The microbeads may be metallised, optionally with a coating ofaluminium, the silicate and/or silane being superposed on the metallisedbeads and the silane where present being superposed on the silicatewhere present.

Also within the scope of the invention is an ink incorporating suchmicrobeads and substrates such as fabrics coated or printed with inks inaccordance with the various aspects of the invention.

For certain applications, notably where printed or coated withretroreflective inks, for example for backdrops and special effectsscreens in film and television studios, it is desirable that fabricsused are fireproof, or fire retardant.

The specialised nature of some retroreflective inks, however, raisesproblems in connection with many normally fireproof or fire retardantfabric materials.

Another aspect of the invention is concerned with a fireproof or fireretardant fabric printed or coated with retroreflective ink that isparticularly satisfactory as a backdrop or screen in the applications inquestion.

The invention comprises a fireproof or fire retardant fabric printed orcoated with a retroreflective ink which comprises retroreflectiveelements in a polymeric matrix, the fabric comprising a structuralcomponent that chars before it melts.

The fabric may be made fireproof or fire retardant by application of afire retardant agent, such as the commercially available Proban® orPyrovatex®, to cellulosics, or it may be naturally fireproof or fireretardant, such as an aramid.

The ink is desirably non-burning, at least once applied to the fabric.The polymeric matrix may comprise polyvinylidene chloride (e.g. in thecase of an aqueous-based ink), or polyvinyl chloride or othernon-flammable plastisol.

Examples of suitable inks for this purpose are given hereinafter inTables 2 and 3.

Substrates coated with inks in accordance with various aspects of thepresent invention may find use in a variety of applications such asflexible tape having a retroreflective coating, for instance tape asused in defining boundary lines and/or cordoning off areas such as crimescenes, construction sites, road works and other hazards.

Another important application is retroreflective materials for use asstudio background material for chroma-keying and like purposes, asdisclosed in GB-A-2312565 and GB-A-2321814 the disclosures of which areincorporated herein by this reference. Thus, a substrate in the form ofa flexible sheet material may be coated or printed with an ink inaccordance with the present invention to produce a studio backgroundmaterial exhibiting a normalised retro-reflectivity of at least about ¼at an angle of incidence of at least 60 degrees to the normal, i.e. asdescribed in GB-A-2312565 and GB-A-2321814.

A substrate provided with a retroreflective coating in accordance withthe present invention may be provided with an additional coating orcoatings for protecting the retroreflective coating against scuffingand/or moisture (i.e. a water repellant coating), e.g. a fluoropolymercoating applied over the retroreflective coating. An anti-static coatingmay also be applied to the substrate. Alternatively, instead of coatingthe substrate with such coatings after printing or coating the substratewith retroreflective ink, the ink may incorporate ingredients which willconfer anti-scuffing, water repellant and/or anti-static properties.

The substrate may be selected from a wide range of materials includingtextile fabrics (e.g. woven or knitted) such as cotton, polyesters,nylons, silk, wool, viscose and acrylics.

Inks and methods for making them, according to the invention, will nowbe described with reference to the accompanying drawings, in which FIG.1 is a diagrammatic illustration of the production of metallised beads;and FIG. 2 is a block diagram of a process for making an ink.

Examples of ink formulations according to the invention are given inTables 1 to 4. TABLE 1 Inks based on a acrylic copolymer binder systemand (3-aminopropyl) silanetriol coupling agent Ingredient/Ink referenceC202 C205 C208 Urea (Humectant) 10 10 10 Water 154 179 179 Ammoniumphosphate buffer 20 20 20 Alcoprint PDN (Dispersant) 2 2 2 Agitan 218(Defoamer) 2 2 2 Alcoprint PT21 (Thickening agent) 8 8 8 2,3 Propanediol (Humectant) 25 25 25 Alcoprint PFL (Trimethoxymethyl 15 15 15melamine cross-linking agent) Alcoprint PSM (Softening agent) 30 30 30Alcoprint PBA (Acrylic copolymer 300 225 225 binder) Ammonium hydroxide1 1 1 Silquest VS-142 (3-aminopropyl 25 25 25 silanetriol couplingagent) [20% in water] Alcoprint PT21 (Thickening agent) 6 3 4.6Metallised beads (40 micron) treated 400 450 400 with sodium silicateand Silquest A-1170 (Bis[trimethoxysilylpropyl] amine) Nonmetallisedbeads (40 micron) — — 50 treated with sodium silicate and SilquestA-1170 Total 997 995 996.6 Binder volume % 12 9 9 Bead volume % 16 18 18Binder volume/bead volume % 75 50 50 Viscosity 20.7 16.2 23.2Temperature 16.6 16.6 16.6 pH 8.4 8.9 8.8

TABLE 2 Inks based on a polyvinylidene chloride copolymer binder systemand (3-aminopropyl) silanetriol coupling agent Ingredient/Ink referenceV246 V248 V251 Urea (Humectant) 10 10 10 Water 128 288 288 Ammoniumphosphate buffer 20 20 20 Emulsifier WN (Dispersant) 3 3 3 Agitan 218(Defoamer) 2 2 2 Alcoprint PT21 (Thickening agent) 8 8 8 2,3 Propanediol (Humectant) 25 25 25 Polidene 33-048 (Binder) 273 163 163 Ammoniumhydroxide 1.4 1.4 1.4 Silquest VS-142 (Coupling agent) 25 25 25 [20% inwater] Alcoprint PT21 (Thickening agent) 3 5 3 Metallised beads (40micron) treated 500 450 400 with sodium silicate and Silquest A-1170Non-metallised beads (40 micron) — — 50 treated with sodium silicate andSilquest A-1170 Total Weight of Ink (g) 998.4 1,000.4 998.4 Bindervolume % 15 9 9 Bead volume % 20 18 18 Binder volume/bead colume % 75 5050 Viscosity (pascals) 25.6 14.2 12.3 Temperature (° C.) 17.7 17.6 17.2pH 8.6 8.7 8.7

TABLE 3 Inks based on a polyvinylidene copolymer binder system and acombination of (3-aminopropyl) silanetriol and blocked hexamethylenediisocyanate trimer coupling agents Ingredient/Ink reference V253 V254V257 Urea (Humectant) 10 10 10 Water 91 183 183 Ammonium phosphatebuffer 20 20 20 Emulsifier WN (Dispersant) 2 2 2 Emulsifier HVN(Dispersant) 2 2 2 Agitan 218 (Defoamer) 2 2 2 Alcoprint PT21(Thickening agent) 9.3 8 8 2,3 Propane diol (Humectant) 25 25 25Polidene 33-048 (Binder) 273 181 181 Ammonium hydroxide 1.4 1.4 1.4Silquest VS-142 (Coupling agent) 25 25 25 [20% in water] Trixene BI 7986(Coupling agent) 40 40 40 Alcoprint PT21 (Thickening agent) — — —Metallised beads (40 micron) treated 500 500 400 with sodium silicateand Silquest A-1170 Non-metallised beads treated with — — 100 sodiumsilicate and Silquest A-1170 Total Weight of Ink (g) 1,000.7 999.4 999.4Binder Volume % 15 10 10 Bead Columes % 20 20 20 Binder Volume/BeadVolume 75 50 50 Ratio % Viscosity (pascals) 22.5 22.1 21.2 Temperature(° C.) 19.3 19.0 19.0 pH 8.4 8.3 8.4

TABLE 4 Inks based on a polyurethane binder system and a blocked 1,6Hexamethylene diisocyanate trimer coupling agent Ingredient/Inkreference P96 P98 P102 Urea (Humectant) 10 10 10 Water 62 187 187 SodiumPhosphate Buffer 10 10 10 Emulsifier WN (Dispersant) 3 3 3 Agitan 218(Defoamer) 2 2 2 Alcoprint PT21 (Thickener) 3.0 3.1 3.0 2,3 Propane diol(Humectant) 25 25 25.1 Alcoprint PSM (Softener) 30 30 30 Witcobond 769(Binder) 300 225 226 Trixene BI-7986 (Coupler) 50 50 50 Alcoprint PT21(Thickener) 0.7 4.0 3.0 Metallised beads treated with 500 450 400sod.silicate and Silquest A-1170 Non-metallised beads treated with — —70 sod.silicate and Silquest A-1170 Total Weight of Ink (g) 993.7 999.11,019.1 Binder Volume % 12 9 8.8 Bead Volume % 60 18 18.5 BinderVolume/Bead Volume 60 50 47.9 Ratio % Viscosity (pascals) O/R 31.0 32.0Temperature (° C.) 18.8 18.2 18.5

Generally speaking, the ingredients are added in the tabulated ordergiven in Tables 1 to 4. The thickener is added in two stages. Pigment,not tabulated, is added at the end in suitable quantity to yield thedesired colour.

Viscosities were measured with a Brookfield viscometer using a number 5spindle rotating at 10 rpm.

Table 5 lists the chemical nature and sources of proprietary productsused in the inks of Tables 1 to 4. TABLE 5 Proprietary Ink ComponentProduct Chemical Nature Supplier Binder Alcoprint PBA Aqueous emulsionof an Allied Colloids acrylic copolymer Polidene 33-048 Aqueous emulsionof a Scott Bayer vinylidene chloride/ acrylate copolymer Witcobond 769Water based polyurethane Baxenden dispersion Cross-linking/ AlcoprintPFL Trimethoxymethyl Allied Colloids coupling agent melamine SilquestVS-142 3-Aminopropyl OSi Specialities/ silanetriol Ambersil Ltd.Silquest A-1170 bis-trimethoxysilylpropyl) OSi Specialities/ amineAmbersil. Ltd. Trixene BI-7986 Blocked 1,6 hexamethylene Baxendendiisocyanate trimer Softening agent Alcoprint PSM Allied ColloidsThickening agent Alcoprint PT21 Dispersion of an acrylic Allied Colloidscopolymer in light mineral oil Dispersant Alcoprint PDN Aqueous solutionof an Allied Colloids anionic acrylic polymer EmulsifierWN Nonionicarylpolyglycol Bayer ether Emulsifier HVN BASF Defoaming agent Agitan218 Munzing Chemie

Retroreflective microbeads are made, according to one aspect of theinvention, by a process which is generally similar to the one that hasbeen used commercially for many years, namely by embedding glassmicrospheres in an adhesive layer on a substrate and coating the exposedsurface of the microspheres with an aluminium layer in a vacuummetalliser. There are, however, subtle, but important differences. Themethod according to the invention, which is novel and inventive per sefor the manufacture of hemispherically coated microbeads, regardless ofany ink formulation in which they will be used is illustrated by way ofexample in FIG. 1.

A carrier material 11, which is for example a polyester film, suppliedon a reel 11 a, which may contain, say, 1000 m of film of width 1500 mm,is coated by contact with a lick roller 12 dipping into a bath 13 withan 18 micron layer 14 of a styrene/butadiene type adhesive 15, thecoating thickness being determined e.g. by a doctor blade/rollerarrangement 16.

Beads 17 (see inset to FIG. 1) are scattered on the adhesive layer 14from a hopper 18 and pressed into the adhesive layer 14 by a rollerarrangement 19. Excess beads are removed e.g. by suction arrangement 20.

Glass beads of refractive index 1.9, size 40 microns are used, and,after the roller arrangement 19, appear, in cross-section, as shown inthe inset.

The beaded carrier material 11 is then passed through a vacuummetalliser 21 to be coated with aluminium to a thickness of about 0.3microns. The material 11, wound on a reel, is placed in the vacuummetalliser and run off on to a take-up reel to which it is secured; thenthe metalliser is evacuated and the aluminium source energised and thematerial passed reel-to-reel to expose it to the aluminium vapour. Thecoated, beaded carrier 11 is then passed through a bath 22 of aqueoussolution (1%) of citric acid at a temperature of 40-50° C., passing overa series of rollers 23 to provide a dwell time in the bath of severalminutes. The material 11 also passes over an ultrasonic plate 24 whichaids release of the microbeads which fall to the bottom of the bath 22.At the end of the run of 1000 m of carrier 11, the microbeads are suckedout of the bottom of the bath 22, rinsed with water and dried.

The effect of the citric acid bath is to cause the styrene/butadieneadhesive to lose its tack and release the microbeads. The material 11regains its tack on drying, and can be re-used for further runs of beadmanufacture without the need for further coating. The citric acid bath22 can likewise be reused without replenishment of the citric acid.

Prior to coating, the glass beads are pre-treated with a dilute aqueoussolution of stannous chloride, followed by drying and resieving. It isfound that this gives significant improvement in the durability of thereflectivity of a printed design.

After coating, the beads are treated with a dilute aqueous solution ofsodium silicate. It is thought that the treatment passivates thealuminium coating, reducing its susceptibility to attack in aqueousenvironments, while, at the same time, the sodium silicate reacts withthe titanium/barium glass and/or the aluminium increasing the number ofreactive sites on the surface of the coated microbeads that areavailable for reaction with the coupling agent in the ink.

If this sodium silicate treatment is carried out close to themetallisation process, the beads from that process can be used afterrinsing but before drying. About 40 kg wet metallised beads (containingsome 10 kg water) are mixed with a solution of 20 kg water containing1.4 kg sodium silicate and stirred for 5 minutes. The beads are thenallowed to settle, the sodium silicate solution decanted off, the beadsrinsed with tap water, with a final rinse in deionised water.

Significant improvement in washfastness, especially with low (e.g. below0.5%) levels of certain coupling agents in the formulation (whichconsiderably improves shelf life), is obtained by further treatment ofthe metallised beads with amino silanes, significantlybis-[gamma-(trimethoxysilyl) propyl] amine.

The combined effect of these bead preparation treatments is to providean ink with a shelf life well in excess of 12 months yet which exhibitsinsignificant loss of retroreflectivity after multiple washings at 40°C., even if the amount of coupling agent is as low as 0.5%.

FIG. 2 is a block diagram of production steps for a typical inkaccording to the invention, the steps being:

-   -   30 Glass microbead production, with any necessary sieving to a        desired size range—about 40 microns is an ideal size;    -   31 Stannous chloride pre-treatment, drying;    -   32 Metallising;    -   33 Recovery in citric acid solution;    -   34 Rinsing;    -   35 Drying;    -   36 Sodium silicate treatment of metallised beads;    -   37 Rinsing;    -   38 Amino silane pre-treatment;    -   39 Mixing liquid carrier medium;    -   40 Add treated metallised (and, if desired, unmetallised) beads        to carrier medium;    -   41 Add pigment;

Ink formulations detailed herein, formulated by the methods described,operating as one-pack systems, have long shelf lives, being usable aftermore than six months, in many cases after more than a year afterformulation (based on accelerated ageing measurements at elevatedstorage temperatures). They show higher initial retroreflectivities atthe lower binder/bead volume ratios made possible by the variousmeasures described.

Washfastness and abrasion resistance are acceptable with binder volumesas low as 9%—reducing binder content in the formulation containingpolyvinylidene chloride and Trixene reases abrasion resistance.

The various novel ingredients and combinations of ingredients each havetheir contributions to make in connection with the production of onepack inks and while the importance of a binder combined with a couplingagent reacting only at elevated temperature has been regularly noted, itis not intended to suggest that that might be the only novel andinventive subject matter disclosed herein. The pre-treatment of thebeads both before and after metallisation also has profound effects evenwith the binder/coupler systems and is of advantage also in thepreparation of inks for printing on substrates which will not withstandelevated temperatures. Here it is necessary to resort to a two-packsystem, with the coupling agent mixed into the ink just before printing.A reactive polyisocyanate may be used as a coupling agent in suchcircumstances. A two-pack arrangement is, of course, more convenient touse than the old three-pack system, and is made possible by beadpre-treatment.

Where unmetallised beads are added—giving the effect, quite obviously,of reducing overall retroreflectivity, but reducing the greynessassociated with metallised beads and therefore enhancing the colourbrightness of pigmented inks, the unmetallised beads also benefit fromthe bead pre-treatment, particularly treatment with silicate and silane.

Unmetallised beads may also be used in similar formulation, and havinghad similar pre-treatment, without metallised beads but with flakeparticles having a mirror-like finish. Such a coating composition, saidto be suitable for application by brushing, was described in U.S. Pat.No. 3,835,087, Searight et al, issued 10 Sep. 1974, and printing ink ofthis description is commercially available.

According to the present invention, in another aspect, one-pack inkscontaining unmetallised glass microspheres and flake particles comprisea liquid carrier medium including binder chemicals for attaching themicrobeads and flake particles to a substrate to which the ink is to beapplied and a coupling agent which couples the microbeads andcross-links the binder chemicals, characterised in that the couplingagent is unreactive except at elevated temperature at which the ink ofthe substrate is cured.

Binder and coupler systems as described above are suitable, and themicrobeads benefit in the same way from the sodium silicate and aminosilane pre-treatment—the stannous chloride pre-treatment is unnecessary.

A preferred flake material is Iriodin 123—mica flake coated withtitanium dioxide, supplied by Merck. The optimum particle size is 5-35microns, and the flake may be present in an amount about 7.5% by weight.

Mean glass microbead size may be 60 micron—larger beads, e.g. up to 70micron and larger, may be used but may not be suitable for finer screenprinting mesh sizes. Good quality, e.g. 1.9 refractive index, beads givebetter results than lower refractive index beads, and best results areobtained using 60 micron TSTF (twice sieved twice fired) beads.

Coloured reflectivity can be achieved by using interference pigments(Iriodin 200 series), while gold lustre mica pigments (Iriodin 300series) and metal lustre pigments (Iriodin 500 series) give interestingeffects particularly when printed on coloured fabrics. Table 6 listsingredients for a range of such inks. TABLE 6 Ingredient/Ink referenceNMB155 NMBI82 NMB185 NMB191 Urea (Humectant) 10 10 10 10 Water 79 134 9491 Ammonium phosphate buffer 20 20 20 — Sodium phosphate buffer — — — 10Emulsifier WN (Dispersant) — 3 2 3 Emulsifier HVN (Dispersant) — — 2 —Alcoprint PDN (Dispersant) 2 — — — Agitan 218 (Defoamer) 2 2 2 2Alcoprint PSM (Softener) 30 — — 30 Alcopriny PT21 (Thickener) 4 4.8 3.33 2,3 Propane diol (Humectant) 25 25 25 25 Alcoprint PFL (Cross-linker)15 — — — Alcoprint PBA (Binder) 300 — — — [acrylic] Polidene 33-048(Binder) — 300 300 — [polyvinylidene chloride] Witcobond 769 (Binder) —— — 300 [polyurethane] Trixene BI-7986 (Coupling — — 40 50 agent)Ammonium hydroxide 1 1.4 1.4 — Silquest VS-142 (Coupling agent) 25 25 25— [20% in water] Alcoprint PT21 (Thickener) 3.5 — — 1 Iriodin 123 [Micacoated with titanium 75 75 75 75 dixoide] Beads (60 micron) treated with400 400 400 400 sod.sil. + A-1170 Total weight (g) 991.5 1000.2 999.71000.0 Viscosity (pascals) 23.6 pH 8.5

1-56. (canceled)
 57. A combination of ingredients forming aretroreflective ink, the combination comprising metallisedretroreflective elements, microbeads additional to said retroreflectiveelements and/or constituting said retroreflective elements at least inpart, binder chemicals for attaching the retroreflective elements andmicrobeads to a substrate to which the ink is to be applied, a couplingagent for coupling the microbeads and cross-linking the binderchemicals, and a buffer, the coupling agent being unreactive and uncureduntil a curing step is carried out and reactive when the curing step iscarried out during which a temperature of the substrate and ink appliedto the substrate is elevated to between 60 and 200° C., the couplingagent having a storage life of not less and about 3 months and beingunreactive except at elevated temperature of the curing step, thecoupling agent being selected from the group consisting of an aminoalkylsilanetriol and a blocked polyisocyanate.
 58. The combination ofingredients according to claim 57, wherein the buffer is a phosphatebuffer.
 59. The combination of ingredients according to claim 58,wherein the phosphate buffer is an ammonium phosphate buffer.
 60. Thecombination of ingredients according to claim 58, wherein the phosphatebuffer is a sodium phosphate buffer.
 61. The combination of ingredientsaccording to claim 57, wherein the binder is a polyvinylidene chloridecopolymer and the coupling agent is an aminoalkyl silanetriol.
 62. Thecombination of ingredients according to claim 57, wherein the binder isan acrylic copolymer and the coupling agent is an aminoalkylsilanetriol.
 63. The combination of ingredients according to claim 57,wherein the binder is polyurethane and the coupling agent is a blockedhexamethylene diisocynate trimer.
 64. The combination of ingredientsaccording to claim 57, wherein the binder is a non-flammable plastisol.65. The combination of claim 64, wherein the non-flammable plastisol ispolyvinylidene chloride.
 66. The combination of claim 64, wherein thenon-flammable plastisol is polyvinyl chloride.
 67. The combination ofingredients according to claim 57, additionally including a humectant.68. The combination of ingredients according to claim 67, wherein thehumectant is urea.
 69. The combination of ingredients according to claim67, wherein the humectant is a combination of urea and 2,3 propane diol.70. The combination of claim 57, wherein the combination comprises a onepack retroreflective ink.
 71. The combination of claim 57, wherein atleast some of the microbeads are without the retroreflective elements.72. The combination of claim 57, wherein a polyvinylidene chloridecopolymer is the binder chemical and a mixture of an aminoalkylsilanetriol and a blocked hexamethylene diisocyanate trimer is thecoupling agent.
 73. The combination of claim 57, further comprising oneor more components selected from the group consisting of: pigment,dispersant, defoamer, thickening agent, cross-linking agent, softeningagent, carbon black, UV absorbing material, anti-scuffing agent, asilicone or fluoropolymer, light spill-suppressing agent, anti-staticagent, water repellent agent, a silicone, and a fluoropolymer.
 74. Thecombination of claim 57, wherein the volume ratio of the binder to themicrobeads is equal to or less than 50%.
 75. The combination of claim57, wherein essentially all of the microbeads are unmetallised and theretroreflective elements include reflective flake particles.
 76. Thecombination of claim 57, wherein the binder forms at least part of aliquid carrier medium for the retroreflective elements or microbeads.77. The combination of claim 57, wherein the binder chemicals,retroreflective elements and microbeads are comprised of a one-packretroreflective ink or a two-pack retroreflective ink having thecoupling agent as the second pack.
 78. The combination of claim 77,wherein the two-pack ink includes a reactive polyisocyanate or analkoxysilyl alkyl derivative.
 79. The combination of claim 57, whereinthe microbeads are metallised with an aluminum coating that issuperposed on a stannous chloride pre-treatment.
 80. The combination ofclaim 79, wherein the metallised microbeads are treated with a solutionof a silicate, followed by treatment with a silane.
 81. The combinationof claim 80, wherein the microbeads have at least one of the followingcharacteristics selected from the group consisting of: a refractiveindex in the range of about 1.8 to 2.2, a median size of the microbeadsin the range of about 10 to 100 microns and the microbeads are composedof titanium glass or barium glass.
 82. The combination of claim 79,wherein the metallised microbeads are treated with an amino silane. 83.A composition that a is one-pack or a two-pack retroreflective ink whichis comprised of the combination claimed in claim
 57. 84. The compositionof claim 83, wherein the ink has a viscosity of between 10 and 30 Pascalseconds at room temperature.
 85. The composition of claim 83, whereinthe retroreflective ink is water-based.
 86. The composition of claim 85that is suitably formulated for screen printing.
 87. The composition ofclaim 83, wherein the ink has a viscosity that is less than or equal toabout 40 Pascal seconds at room temperature.
 88. The composition ofclaim 57, wherein the coupling agent has a storage life of not less thanabout 3 months and is unreactive except at elevated temperature ofbetween 130 and 180° C. at which the one-pack retroreflective inkprinted on the substrate is cured.
 89. A method for making a one-packretroreflective ink comprising the steps of: (a) making metallisedmicrobeads; and (b) suspending the microbeads in a liquid carriermedium, the liquid carrier medium being comprised of binder chemicalsfor attaching the microbeads to a substrate to which the ink is to beapplied, a coupling agent which couples the microbeads and cross-linksthe binder chemicals, and a buffer, the one-pack retroreflective inkhaving a storage life of not less than about 3 months and the couplingagent being unreactive and uncured until a curing step is carried outand reactive when the curing step is carried out during which atemperature of the substrate and ink applied to the substrate iselevated to between 60 and 200° C., the coupling agent having a storagelife of not less than about 3 months and being unreactive except atelevated temperature of the curing step, the coupling agent beingselected from the group consisting of an aminoalkyl silanetriol and ablocked polyisocyanate.
 90. The method of claim 89, wherein step (a)includes applying an aluminium coating to the microbeads.
 91. The methodof claim 90, wherein step (a) includes pre-treating the microbeads withstannous chloride prior to application of the aluminium coating.
 92. Themethod of claim 89, wherein step (a) includes treating the microbeadswith a silane or an amino silane prior to inclusion in the ink.
 93. Themethod of claim 89, wherein step (a) includes hemisphericallymetallising the microbeads in a vacuum metallising process in which themicrobeads are held on a film with an adhesive coating for transportthrough the metallising process, the adhesive coating is comprised ofstyrene-butadiene type adhesive.
 94. The method according to claim 93,wherein step (a) includes passing the film through an aqueous solutionof citric acid after metallisation.
 95. The method of claim 93, whereinstep (a) includes ultrasonically treating the film to assist in releaseof the microbeads from the adhesive.
 96. The method of claim 91, whereinstep (a) includes treating the microbeads with a dilute aqueous solutionof stannous chloride.
 97. The method of claim 96, wherein step (a)includes treating the microbeads prior to inclusion in the ink with asilicate.
 98. The method of claim 97, wherein step (a) includes treatingthe microbeads with an amino silane after the silicate treatment. 99.The method of claim 98, wherein the microbeads have at least one of thefollowing characteristics selected from the group consisting of: arefractive index in the range of about 1.8 to 22., a median size of themicrobeads in the range of about 10 to 100 microns and the microbeadsare composed of titanium glass or barium glass.
 100. The method of claim89, wherein step (b) includes preparing the liquid carrier medium fromthe binder chemicals and the coupling agent before suspending themicrobeads in the liquid carrier medium.
 101. The method of claim 100,wherein the liquid carrier medium of step (b) includes additivesselected from the group consisting of: pigment, dispersant, defoamer,thickening agent, cross-linking agent, softening agent, carbon black, UVabsorbing material, anti-scuffing agent, silicone, fluoropolymer, lightspill-suppressing agent, anti-static agent and water repellent agent.102. The method of claim 101, wherein step (b) includes adding athickener to the liquid carrier medium before or after the addition ofthe binder chemicals and coupling agent.
 103. A composition of an inkproduced by the method of claim
 89. 104. A composition of a substratecoated or printed with a composition of claim
 103. 105. The compositionof claim 104, wherein the substrate is a screen for displaying projectedimages or a studio background for chroma-keying applications.
 106. Thecomposition of claim 104, wherein the substrate is a flexible tape. 107.The method of providing a substrate having a retroreflective coating,comprising the steps of: applying to the substrate an ink as claimed inclaim 103, wherein the ink is formulated as a one-pack retroreflectiveink and the coupling agent is activated after the ink is printed orcoated on to the substrate.
 108. The method of claim 107, wherein thecoupling agent is activated by curing the ink coating at elevatedtemperature.
 109. The method of claim 107, wherein the coupling agent isactivated by UV light or other high energy radiation during or after theprinting process.
 110. The composition of claim 103, wherein the ink isa retroreflective one-pack ink having a storage life of not less thanabout 3 months.
 111. The composition of claim 110, wherein theretroreflective one-pack ink has a viscosity of between about 10 and 30Pascal seconds after storage of not less than about 3 months.
 112. Thecomposition of claim 110, wherein the retroreflective one-pack inkapplied to the substrate and cured has a laundering durability such thatthe retroreflectivity is not reduced by more than about 40% when thesubstrate is in the form of a cotton, nylon or polyester fabric andlaundered for 5 cycles in accordance with ISO 6330, method 5A.
 113. Themethod of claim 89, wherein the coupling agent has a storage life of notless than about 3 months and is unreactive except at elevatedtemperature of between 130 and 180° C. at which the one-packretroreflective ink printed on the substrate is cured.
 114. The methodof claim 89, wherein the liquid carrier medium of step (b) includes aphosphate buffer.
 115. The method of claim 114, wherein the phosphatebuffer is an ammonium phosphate buffer.
 116. The method of claim 114,wherein the phosphate buffer is a sodium phosphate buffer.
 117. Themethod of claim 89, wherein the liquid carrier medium of step (b)additionally includes a humectant.
 118. The method of claim 117, whereinthe humectant is urea.
 119. The method of claim 117, wherein thehumectant is a combination of urea and 2,3 propane diol.
 120. The methodof claim 89, wherein the binder of the liquid carrier medium is anon-flammable plastisol.
 121. The method of claim 120, wherein thenon-flammable plastisol is polyvinylidene chloride.
 122. The method ofclaim 120, wherein the non-flammable plastisol is polyvinyl chloride.123. A combination of ingredients forming a retroreflective ink, thecombination comprising retroreflective elements, microbeads additionalto said retroreflective elements and/or constituting saidretroreflective elements at least in part, binder chemicals forattaching the retroreflective elements and microbeads to a substrate towhich the ink is to be applied, and a coupling agent for coupling themicrobeads and cross-linking the binder chemicals, the coupling agentbeing unreactive and uncured until a curing step is carried out andreactive when the curing step is carried out during which a temperatureof the substrate and ink applied to the substrate is elevated to between60 and 200° C., the coupling agent having a storage life of not lessthan about 3 months and being unreactive except at elevated temperatureof the curing step, the coupling agent being selected from a groupconsisting of an aminoalkyl silanetriol and a combination of aminoalkylsilanetriol and blocked polyisocyanate and wherein the ink retains aviscosity of between 10 and 30 Pascal seconds for not less than 3months.
 124. A method for making a one-pack retroreflective inkcomprising the steps of: (a) making metallised microbeads; and (b)suspending the microbeads in a liquid carrier medium, the liquid carriermedium being comprised of binder chemicals for attaching the microbeadsto a substrate to which the ink is to be applied and a coupling agentwhich couples the microbeads and cross-links the binder chemicals, theone-pack retroreflective ink having a storage life of not less thanabout 3 months and the coupling agent being unreactive and uncured untila curing step is carried out and reactive when the curing step iscarried out during which a temperature of the substrate and ink appliedto the substrate is elevated to between 60 and 200° C., the couplingagent having a storage life of not less than about 3 months and beingunreactive except at elevated temperature of the curing step, thecoupling agent being selected from a group consisting of an aminoalkylsilanetriol and a combination of aminoalkyl silanetriol and blockpolyisocyanate; and wherein the ink retains a viscosity of between 10and 30 Pascal seconds for not less than 3 months.